A diesel engine system generally comprises an exhaust gas recirculation (EGR) system that works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. In modern diesel engines, the EGR gas is cooled through a heat exchanger to allow the introduction into the engine of a greater mass of recirculated gas and to lower gas temperature. The EGR system is primarily used in order to reduce emissions, especially of NOx.
Current European and US legislation require that the Engine Control Unit (ECU) on board has also a monitoring function of the EGR cooler efficiency. Specifically, EGR cooler efficiency is measured by means of two temperature sensors, one at the EGR cooler inlet in order to measure the inlet temperature Tinlet and the other at the outlet of the EGR cooler in order to measure the outlet temperature Toutlet. With this two sensors approach, the EGR cooler efficiency η=(Tinlet−Toutlet)/(Tinlet−Toutlet) value can be measured and, when it is inferior to a predetermined threshold, an alarm or any other indication may be given in order to signal that the performance of the EGR cooler is degraded. The drawback of this prior art approach is that two temperature sensors are needed for the EGR cooler efficiency degradation detection and these sensors have generally a high cost.
At least one aim of the embodiments of the invention is to provide a methodology that allows Diesel controller to have a monitoring function for the EGR cooler efficiency and to comply with legislation, while at the same time being able to reduce overall costs. A further aim of the invention is to avoid usage of temperature sensors across the EGR cooler, in order to realize a substantial cost saving. In addition, other desirable features and characteristics will become apparent from the subsequent summary or detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.